Flood Forecasting: A Data Collection Partnership

Peter Corrigan, Service Hydrologist

The National Weather Service in Blacksburg is responsible for issuing flood and flash flood forecasts for the numerous rivers and streams in our 40-county, 3-state area of responsibility.  Gathering the data which underpins this effort is a multi-federal agency task which derives additional support from state, county, local and private entities interested in protecting life and property from the destructive effects of flooding.

In order to forecast flooding meteorologists and hydrologists at the NWS need to know how much rain has fallen over specific watersheds and how streams and rivers within the watershed are responding to the runoff from heavy rain or snowmelt. To accomplish this, the NWS in Blacksburg monitors literally hundreds of rain and stream gages many on a near real-time basis.  There are several important data networks that support this endeavor which will be briefly reviewed below.

The vast majority of river and stream gages in our area and across the nation are operated by the United States Geological Survey (USGS) which is part of the U.S. Department of the Interior.  Each state in our forecast area (VA, WV, NC) has a USGS office which is responsible for installing new gages in their area and maintaining the existing networks. These networks form the backbone of the NWS flood warning program in addition to providing water information to a wide variety of users. Flood forecasting is truly a partnership between the NWS and USGS whereby the NWS provides river and flood forecasts to the public using stage and flow data from the USGS networks across the country.  The following link provides an overview of the NWS-USGS partnership in flood forecasting: http://water.usgs.gov/wid/FS_209-95/mason-weiger.html. In addition it should be pointed that the USGS itself also has partnerships with numerous cities, towns and private companies (such as dam owners) in order to share the cost of operating river gages. These gages may be critical to allow forecasts to be made for that location. An excellent example is the City of Roanoke, VA which partners with the USGS on gages for the Roanoke River which can affect the city. To learn more about USGS water programs in general go their water web site: http://water.usgs.gov/.

The U.S. Army Corps of Engineers is another valuable federal partner in the flood forecasting efforts of the NWS. Three different Corps districts operate within the Blacksburg NWS area, including the Wilmington, NC, Norfolk, VA and Huntington, WV districts.  Each of these Corps districts operate one or more important dams projects in our area for which substantial amounts of hydrometeorological data are required for the efficient and safe operation of the projects. The NWS uses this data as well to enhance its own flood forecasting efforts and coordinates with the Corps on the data networks involved. The Corps web site: www.usace.army.mil/ provides links to the various Divisions and Districts of the Corps and to descriptions of the specific dam projects in this area.

Another important network is the Integrated Flood Observing and Warning System (IFLOWS) which is a network of rain and stream gages operated at the state level in all three of the states in our area. This network was originally developed by the NWS in the late 1970s in conjunction with several Appalachian states where a series of severe flash floods occurred. The network has expanded greatly over the years in the eastern U.S., mainly in mountain areas susceptible to flash flooding. All three states in our area are important partners in the IFLOWS network and provide critical support and maintenance functions. At this writing the network is in the midst of a major overhaul in the data delivery architecture but the web site http://afws.net/ still contains the data and has more detailed information on how the network operates.

Other federal agencies also make important contributions to the data collection effort,  including  the United States Forest Service (USFS) with its Remote Automated Weather Stations (RAWS).  These are located primarily in the mountains in order to monitor fire weather potential but are also used for precipitation analysis and hence can support flood forecasting.  The Federal Aviation Agency (FAA) is another that provides data through its Automated Weather Observing System (AWOS). Although primarily used in support of aviation forecasting, some AWOS sites have rain gages.

In recent years many television stations including several in our area have started local weather observing networks at schools, businesses and parks. These may also provide rainfall data, which can be used in NWS hydrologic and other forecasts. Another relatively new source of precipitation data being used by the NWS is the Community Collaborative Rain, Hail and Snow network (CoCoRaHS). This is a voluntary network begun in Colorado after a major flood in 1997, which has been expanding across the U.S. since that time. All three of our states are part of the CoCoRaHS network which consists of public volunteers entering daily or very intense precipitation data onto a web site at http://www.cocorahs.org/. This network helps to provide the spatial density of data often needed to provide accurate input to NWS hydrologic models. 

Of course the NWS operates several important networks of its own including the Automated Surface Observing System (http://www.nws.noaa.gov/asos/) or ASOS network at larger airports and the Cooperative Network (http://www.nws.noaa.gov/om/coop/).